We are engaged in the study of photoreceptors from both vertebrate and invertebrate retinas. Ultrastructural properties of photoreceptors are being investigated with both transmission and freeze fracture electron microscopy. Microspectrophotometry of the retina and visual cells allows us to study visual pigments, carotenoids, and other molecules in the photoreceptors and retinal pigment epithelium. The role of ultrastructural changes in the photoreceptors and pigment epithelium which could effect visual transduction, adaptation and retinal physiology are being investigated. The electron microscope and microspectrophotometer are being used in parallel to probe cellular physiology and structure in developing, adult and degenerating visual photoreceptors.